1007 ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2018, Vol. 63, No. 8, pp. 1007–1011. © Pleiades Publishing, Ltd., 2018. Original Russian Text © I.V. Malkov, V.V. Krivetskii, D.I. Potemkin, A.V. Zadesenets, M.M. Batuk, J. Hadermann, A.V. Marikutsa, M.N. Rumyantseva, A.M. Gas’kov, 2018, published in Zhurnal Neorganicheskoi Khimii, 2018, Vol. 63, No. 8, pp. 968–973. Effect of Bimetallic Pd/Pt Clusters on the Sensing Properties of Nanocrystalline SnO 2 in the Detection of CO I. V. Malkov a , V. V. Krivetskii a , D. I. Potemkin b , A. V. Zadesenets c , M. M. Batuk d , J. Hadermann d , A. V. Marikutsa a , M. N. Rumyantseva a, *, and A. M. Gas’kov a a Moscow State University, Moscow, 119991 Russia b Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia c Nikolaev Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia d ЕMАТ, University of Antwerp, Antwerpen, B-2020, Belgium *e-mail: roum@inorg.chem.msu.ru Received February 14, 2017 Abstract⎯Nanocrystalline tin dioxide modified by Pd and Pt clusters or by bimetallic PdPt nanoparticles was synthesized. Distribution of the modifers on the SnO 2 surface was studied by high-resolution transmission electron microscopy and energy dispersive X-ray microanalysis with element distribution mapping. It was shown that the Pd/Pt ratio in bimetallic particles varies over a broad range and does not depend on the par- ticle diameter. The effect of platinum metals on the reducibility of nanocrystalline SnO 2 by hydrogen was determined. The sensing properties of the resulting materials towards 6.7 ppm CO in air were estimated in situ by electrical conductivity measurements. The sensor response of SnO 2 modified with bimetallic PdPt parti- cles was a superposition of the signals of samples with Pt and Pd clusters. DOI: 10.1134/S0036023618080168 INTRODUCTION The concept of chemical modification implies the generation of new active sites on the surface of the semiconductor matrix that would possess specific adsorptivity and reactivity towards gases to be detected [1]. For reducing gases exhibiting no clear-cut acid- base properties (CO, H 2 , hydrocarbons), catalytically active additives such as platinum metals and gold are most efficient. The catalytic modifers do not increase adsorption, but intensify oxidation of the molecules of test gases on the semiconductor oxide surface, which not only enhances the sensor response, but also reduces the temperature of the sensitivity maximum [2–5]. The selectivity of heterogeneous oxidation cat- alysts is determined by the adsorption energy of the reducing gas, the bond energy with the surface oxygen (oxidant), and the bond energies with intermediates and products. The optimal CO oxidation catalysts are Pd and Pt, because the oxygen chemisorption energy of these metals (340–360 kJ/mol) is close to the bond energy between these metals and CO [6, 7]. Palladium and platinum are among the most efficient modifiers for improving the sensing properties of semiconductor metal oxides towards CO [8–10]. The properties of bimetallic catalysts comprising two different metals are now actively studied with the goal to detect a synergistic effect in which the bimetal- lic catalyst activity would exceed the sum of activities of the monometallic analogues [11]. This effect was found for the catalytic activity of palladium and plati- num bimetallic particles towards 1,3-cyclooctadiene hydrogenation [12, 13], methane oxidation [14], and p-nitrophenol reduction [15]. The sensing properties of these systems have been barely studied [16–19]. The purpose of this work was to synthesize nano- crystalline SnO 2 modified by monometallic Pd and Pt clusters and bimetallic PdPt particles, to investigate the distribution of modifers over the SnO 2 surface, and to determine the sensing properties of obtained mate- rials towards carbon monoxide. EXPERIMENTAL Tin dioxide was synthesized by precipitating the α-stannic acid gel from a solution of SnCl 4 ⋅ 5H 2 O with aqueous ammonia. The resulting α-stannic acid gel was separated by centrifugation followed by decan- tation, and washed with distilled water and a 2% solu- tion of NH 4 NO 3 . The centrifugation and washing were repeated many times until the silver nitrate test of the solution for Cl – was negative. The gel was dried in air at 100°C for 24 h and annealed at 500°C for 24 h. The modifers were applied by impregnation (according to water uptake) of nanocrystalline SnO 2 with aqueous solutions of [M(NH 3 ) 4 ](NO 3 ) 2 (M = Pt, Pd) (Sigma- Aldrich). The impregnated powders were dried in air SYNTHESIS AND PROPERTIES OF INORGANIC COMPOUNDS